Environmental factors influence in vitro embryo production of Gir cattle.

The objective of this study was to evaluate the factors influencing in vitro embryo production in the Gir breed in a commercial embryo transfer program in Brazil. Data from 15,894 follicular aspirations in 3682 Gir dairy donors were analyzed and the average number of viable oocytes per donor (VON), proportion of viable oocytes (VOP), blastocyst rate (BLR), and pregnancy rate (PR) were evaluated. First, the collection records were distributed across the seasons, and the results showed that VOP was higher in summer (75.0 %) and spring (74.1 %), while BLR was higher in spring (22.5 %). The donors were subsequently grouped into seven age classes, in which the highest VOP was observed in animals aged 6-8 years (75.2 %), 8-10 years (75.7 %), and 10-12 years (75.9 %). Regarding the BLR, the highest values were observed in donors older than 4 years. Donors were also grouped as heifers or cows, with cows (22.42 %) showing a higher BLR than heifers (20.05 %). Next, the effect of seasons on PR after fresh embryo transfer was evaluated, with spring (43.8 %) and winter (43.5 %) presenting the highest PR. Finally, pregnancy rates were compared following the transfer of fresh or vitrified embryos, showing a higher PR for fresh embryos (41.1 %) than for vitrified ones (34.6 %). Therefore, season, as well as the age and category of Gir donors, influence in vitro production. Additionally, vitrification reduces the survival of in vitro-produced Gir dairy embryos.